Biofeedback approaches have been employed in relaxation therapy utilizing, for example, the respiratory movements of a patient or subject as the monitored variable by which a feedback is provided to the individual so that respiration can be controlled and, as a consequence, a relaxation state can be induced.
In this technique, described, for example, in German patent document DE-OS No. 31 09 026 of May 15, 1984, or the attached brochure relating to respiratory feedback issued by Gesellschaft fur Medizinische Feedback-Gerate GmbH, Gottingen, Germany, and in British Pat. Nos. 1,359,005 and 1,492,875 and German Utility Models DB GM Nos. 7 407 730 and 7 600 359, the respiratory movements of the subject are detected, these movements are transformed into amplified signals by appropriate transducers or electrical circuitry and these respiration and sensing signals are utilized in turn to generate optical or acoustical signals which are applied in a feedback loop to the patient.
This respiratory feedback process can be utilized to generate a relaxed state, i.e. to reduce muscle tone and to reduce brain activity.
However, a measurement of the relaxation state in some absolute or objective manner cannot be effected easily by conventional means. For example, if the relaxation state is to be determined by muscular relaxation, it has been necessary to use electromyelographs while, if the state is determined by brain wave activity, it has been necessary to use electroencephalograms.
Hence the procedures used heretofore for measuring the relaxation state of a patient have involved very expensive and complex equipment and instruments and, moreover, instruments which can only be used with special computers or calculating systems for transforming the electroencepholograph or electromyelograph reading into values representing the degree of relaxation.